Filipe Morais grabbed a late equaliser for Oldham to frustrate League One leaders Charlton, who missed a chance to extend their lead to seven points.
Charlton, who are now unbeaten in 10 matches, opened the scoring when Darel Russell headed in Matt Taylor's cross for his first goal for the club.
Danny Green had earlier fired wide and Bradley Wright-Phillips had twice been denied by Latics goalkeeper Alex Cisak.
However, Oldham claimed a dramatic draw when Morais shot home from 20 yards.
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Charlton boss Chris Powell told BBC London 94.9:
"Teams are not going to make it easy for us and not going to lay down because we're top.
"They frustrated us at times today but we still had chances.
"We remain five points clear like we did this morning and we move on to the Christmas period.
"This season we have had a terrific run but of course everyone has got excited with the wins and they expect wins all the time. We are striving to do it but it hasn't happened today."